The present invention relates to polycarbonate compositions having improved surface hardness, processes for the preparation thereof and the use thereof for the production of shaped articles and extrudates.
Aromatic polycarbonates belong to the group consisting of the industrial thermoplastics. They are distinguished by the combination of the technologically important properties of transparency, heat distortion resistance and toughness.
WO 2007/008390 A2 describes copolycarbonates which contain 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane and optionally 2,2-bis(3-methyl-4-hydroxyphenyl)propane. It is disclosed that windows and other articles comprising this copolycarbonate have particularly good scratch resistance.
WO 2008/008 599 A2 describes the use of polycarbonates which may contain 2,2-bis(3-methyl-4-hydroxyphenyl)propane and/or 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane for the production of flameproofed articles which, with a scratching force of 8 newton, have a scratch depth of less than 20 microns.
Diphenols containing rigid ring bridges in the molecule were described in DE 13 00 267 A. The preparation of linear polycarbonates from these diphenols is also mentioned herein. However, only homopolycarbonates are preparedin the examples. Thus, for example, the diphenol 4,4″-(2-norbornylidene)diphenol, which contains a saturated bicyclic, bridged hydrocarbon ring, is described here. In the document, the object is to provide polycarbonates having improved high-temperature properties. The homopolycarbonates described are said to have a better heat distortion resistance (high glass transition temperature) and solubility in volatile solvents. This is seen as an advantage according to the invention since articles such as films can be obtained therewith, which can be obtained by film casting, or polymer strands can be obtained therefrom by wet or dry spinning from organic solution. U.S. Pat. No. 3,517,071 A, which belongs to the same patent family, also discloses only homopolycarbonates in the examples. For increasing the scratch resistance of the surface hardness of polycarbonate compositions which contain corresponding structural elements in a blend component, the patent provides no teaching with regard to action.
The polycarbonate compositions known from the prior art are, however, not suitable for certain applications in which thermal stability and scratch resistance play an overriding role.
There is therefore the need for a polycarbonate composition which is stable at high temperatures and has increased scratch resistance in combination with the properties which otherwise are equally good.
In the context of this application, polycarbonate compositions (or blends) are understood as meaning mixtures of two or more polycarbonates and optionally provided with additives or polycarbonates with other thermoplastics.
It was therefore the object of the present invention to provide polycarbonate compositions and processes for the preparation thereof, which have a particularly high surface hardness, and polycarbonate compositions for applications in which particular requirements regarding the stability of the surface are set, without having to apply an additional scratch-resistant layer.